Illuminating system for simulating bubbles



March 4, 1969 c. D. SKIRVIN 3,431,465

ILLUMINATING SYSTEM FOR SIMULATING BUBBLES Filed June 20, 1967 Sheet i i I y IN VENTOR.

o ar/zayr March 4, 1969 c. D. SKIRVIN 3,431,455

ILLUMINATING SYSTEM FOR SIMULATING BUBBLES iled June 20, 1967 Sheet z of 2 t 5 23 a, t,,, 4,; I

United States Patent 17 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a system for simulating the appearance of bubbles in a gas-filled tube. The operation of the tube can be controlled so that the shape of the simulated bubbles in the tube can be varied and so that the bubbles will appear to be moving in one direction or the other at a controlled speed. The pressureof the gas in the tube is less than that for producing arcing of the gas in the tube but greater than that for producing glow discharge of the gas in the tube. The circuitry associated with the tube has characteristics of producing a signal at a relatively high frequency with a considerable number of harmonic frequencies in the signal. The fundamental and harmonic components in this signal are operative on the gas at the reduced pressure in the tube to produce ionization of the gas at spaced positions in the tube. The ionization of the gas at the spaced positions in the tube simulates the appearance of bubbles.

This is a continuation-in-part of application Ser. No. 482,493 filed Aug. 25, 1965 by Clifford D. Skirvin for an Illuminating System for Simulating Bubbles.

This invention relates in general to luminescent gas tubes and also to the electronic systems which supply input excitation signals thereto. More particularly, the present invention is concerned with the principles and circuitry for deriving a luminescent tube input excitation signal which increases the lighting efficiency and special effects usefulness of luminescent tubes by creating a bubbling effect in the lighted tube. Moreover, for certain advertising and display uses of the inventive bubble-lighting system, the invention also provides a technique for causing the bubbles to move in either direction along the tube or to appear to remain stationary or to vary in shape between round and oblong. Applicant has found no prior instance in the luminescent gas tube art where lighting has been achieved in a tube in such manner as to give the appearance of formation of bubbles therein.

In the pursuit of the above general aims, this invention includes several new principles in regard to the generation of gas tube input excitation signals which in various combinations will achieve the bubble effect. Thereafter, bubbling can be made to progress slowly along the length of a luminescent gas tube if the input excitation signal has its voltage amplitude, current amplitude and/ or frequency minutely and carefully increased or decreased, the rate of increase governing the rate of progress. At the same time, the waveform of each cycle of the input excitation signal should be of such shape that numerous harmonics of the fundamental frequency are applied across the electrode or electrodes of the gas tube and that the potential of the valence electrons of the gas molecules is lowered as much as possible during the negative swing of each cycle. Thus, illumination can be accomplished by gas ionization, rather than by the arcing technique heretofore used for gas tube lighting. Ionization rather than arcing is important because arcing 3,431,465 Patented Mar. 4, 1969 cannot occur without causing complete illumination of the tube between the electrodes excited, whereas the bubbling effect is the resultant of a form of incomplete illumination. Once illumination by ionization is used in place of arcing, the bubbling effect can be achieved by polarizing the tube electrodes, as the above-described waveform will necessarily do, and then varying input excitation signal current level, voltage, or frequency, or various combinations of these three, to cause the critical power level for illumination to be slightly undercut, so that lighting can occur only in-isolated portions of the tube (i.e.the bubbles) which have positive and negative ends. Between the lighted portions are dark (or only slightly lighted or ionized) areas across which the voltage does not show much change.

As another feature of applicants invention, the lowering of gas pressure in lighting tubes used for creating the bubbling effect below the pressure normally used is found to facilitate achievement of the bubbling effect; for arcing is thereby retarded while ionization is made easier, both due to the thinning out of electron density. For example, in a 10 mm. diameter tube of any normally used length, where 12-15 mm. of mercury gas pressure would be standard in prior lighting applications, 8 mm. of mercury gas pressure would be used in achieving the bubbling effect. The result of this thinning of the luminescent gas is that the individual electrons of the gas molecules have greater freedom of movement and require less energy to ionize or take complete leave of the atomic structure and, accordingly, the power level of the input excitation signal can be lowered.

Since too high an excitation voltage will cause arcing and since increased excitation frequency agitates the electrons more to give the equivalent of higher pressure, the principles of the invention include the lowering of excitation voltage while raising current amplitude (to increase lighting level) and frequency. This combination gives the ionization and non-arcing type illumination necessary when the bubbling effect is being sought, yet at an acceptable level of brilliance.

Additional inventive features appear in the embodiment of the above-mentioned principles in circuitry for producing a bubbling sign input excitation signal from a standard power supply. Experience has shown that most tubes perform poorly at excitation frequencies below 1,000 c.p.s. and will ionize too fast and grow inefficient at frequencies above 30 kilocycles, the latter because electron movement has become too erratic and wide. The circuitry for supplying the input excitation signals, therefore, should have first means for converting a power supply signal into a polarized waveform having a certain fundamental frequency in the 1,000 c.p.s. to 25 kc. range and being rich in harmonics of the fundamental and also having a deep negative excursion at one point in each cycle, and further means for varying the overall power (i.e.-wattage) applied by the circuit across the lighting tube and also the harmonic frequencies of the supply waveform.

The circuit arrangement found to be suitable to operating satisfactorily has a luminescent gas tube coupled in series with a padding capacitor and the secondary of an output transformer. The primary of the output transformer has a first end directly connected to a first terminal of the input power supply while a second end is coupled through a silicon-control rectifier to the second terminal of the input power supply. A capacitor is coupled across the first and second ends of the primary of the output transformer to form a resonant tank. In order to smoothen the input signal to the SCR, a filter arrangement may be connected to the power supply terminals: a capacitor coupled from the first terminal to the second terminal and an inductor coupled in series between the SCR and the second terminal. Switching signals for the SCR may be provided by arranging an RC timing circuit between the second end of the primary of the power transformer and the second terminal of the input power supply. A semiconductor trigger or some other similar firing device is then connected from a point between the resistor and capacitor in the RC timing circuit and the gate of the SCR.

One additional feature of the instant invention is that the resistance in the RC circuit is made variable in order to vary with frequency the power level of metering performed by the SCR. Another feature of the instant invention is the use of a feedback capacitor between the second end of the primary of the output transformer and the gate of the SCR to vary the switching time of the SCR as its frequency of switching varies; for as is well known, a lighting tube improves in efficiency as the frequency of its input excitation signal goes up. Therefore, in order to carefully match the power supplied to the lighting tube with the efficiency of the lighting tube such that the bubbling effect is created at a wide variety of frequencies, the feedback capacitor switches the SCR on harder and faster at low frequencies to pass more power while at the higher frequencies, a slightly slower switch-on time is provided.

In summary then, the invention provides both broad principles and specific circuit techniques for achieving the bubbling effect in luminescent gas tubes, essentially by starving the tube of power to a point just below the minimum power level for complete illumination at the frequency at which the tube is being supplied. In such a situation, the tube can illuminate only partially and this partial illumination turns out to be in the form of bubbleslighted portions having a voltage gradient parallel to the axis of the lighting tube, the lighted portions being separated by relatively dark or unlighted portions having little or no voltage gradient along the length of the tube. In the absence of sufficient power to illuminate the entire tube, a cavitation effect is created whereby only portions of the tube are illuminated and, typically of most equilibruim conditions, these portions are spread evenly and equally throughout the tube. These portions, the bubbles of the instant invention, occupy substantially the full diameter of the tube and can be made oblong or spherical, depending upon the combined effect of the total wattage of power supplied, the gas pressure within the tube, the frequency of the input excitation signal, and the diameter of the tube. Generally speaking, at frequencies around 2,500 to 3,500 cycles per second, the bubbles are oblong; whereas when the frequencies get up toward 25 kilocycles, the bubbles become strictly spherical.

Although the bubbling effect is desirable mainly for special effects or display and advertising purposes to attract attention and to supply an interesting and unusual light rather than merely a functional light source, it has been found that a luminescent tube in which the input excitation signal power has been starved down to the point that the bubbling effect occurs appears more brilliant than it would when it is receiving sufficient power for full illumination. Apparently this is because each separate bubble within the tube functions as a separate tube in its own right, yet has certain advantages over true gas tubes. The first of these advantages is that a luminescent gas tube experiences about a 50 volt drop in input excitation signal voltage at its electrodes, while the bubble tubes, having no electrodes for each bubble, show almost no voltage loss at all across their ends. In addition, because of the very short length of these bubble tubes, they are more efficient (Le-produce more lumens of light per watt of power consumed) than the full length tube would be. It is the combination of these two advantages that insures that the equilibrium condition in a luminescent gas tube will be the formation of bubbles whenever power is starved below the critical amount required for full length illumination.

Having developed the bubble formation effect itself, as

described above, the invention herein disclosed then proceeds to principles for causing the apparent bubbles to move in either direction along the luminescent tube. As stated above, the formation of bubbles is accomplished using a waveform which in each cycle has great richness in harmonics of its fundamental frequency. The apparent movement of the bubbles so formed is then accomplished by shifting the spectrum of the harmonics slightly to cause the bubbles to seek a corresponding new equilibrium position. This shifting of the harmonics can often be accomplished with greatest ease simply by maintaining the amplittude of the input excitation signal the same while shifting its registration or its overall voltage level up or down. This shifting of the registration of the input excitation signal will cause the decay constants of the inductances and capacitances in the circuit to aim toward a slightly different Zero level, with the result that the decay curves and the numerous frequencies of harmonic distortion composing them would be slightly different than for the equilibrium position where the bubbles were standing still. The degree of voltage level shift of the input excitation signal controls the speed of movement and the direction of movement of the bubble formation. In addition, by proper adjustment it has also been found possible to make the hubble formations move in one portion of the gas tube while standing still in another portion or to move in different directions in opposite ends of the tube.

Other features of the instant invention and a better understanding thereof may be had by referring to the following description and claims taken in conjunction with the accompanying drawings, in which:

FIGURE 1 shows the appearance of the bubble formation effect in a luminescent gas tube (FIGURE 1(a)) and the corresponding voltage level across the tube (FIG- URE 1(b));

FIGURE 2 is a schematic diagram of a preferred embodiment of the circuit principles whereby applicant has accomplished the formation of bubbles in luminescent gas tubes; and

FIGURE 3 shows the characteristic waveforms appearing at various points in the circuit of FIGURE 2.

Referring to FIGURE 1(a), the bubbling effect which is accomplished for the first time by the instant invention occurs in a luminescent gas tube 10 having input electrical excitation signal electrodes 12 and 14. Although this principle is not usually recognized or acted upon in luminescent gas tube lighting installations, in every gas tube one electrode is better adapted to act as the anode or more positive electrode while the other is better adapted to act as the cathode or more negative electrode, assuming that the input excitation signal applied across the electrodes is somewhat polarized as it is in the practice of the instant invention. If a polarized waveform is applied in the proper relationship across the tube, that is to saywith its more positive portion applied to the anode electrode of the tube-the tube will perform better than it will if the opposite orientation is used; and in fact, with high frequency polarized waveforms, sometimes the tube will not light at all. The way to ascertain which electrode is the anode and which is the cathode, other than by trial and error, is to determine from an examination of the tube which end contained the pumping orifice during the manufacture of the tube, when the air was evacuated therefrom and a gas was inserted. This end will act as the cathode of the tube because the electron emission that occurs from the cathode will meet with less resistance in the end of the tube which has the greatest vacuum, which is, of course, the end of the tube that was nearest the pumping outlet at the time of evacuation. The end of the tube that was sealed during evacuation will have more gas molecules left in it, and, therefore, will be better adapted to serve as the anode of the tube.

The tube 10 may be pumped with a gas mixture of the neon-argon-mercury vapor variety, preferably to a pressure of about 8 mm. Hg. In such a situation, under the influence of an input excitation signal applied across the electrodes 12 and 14, bubbles of the sort illustrated at 16 and 18 will be created. All the bubbles 16 and 18 will have a diameter approximating the diameter of the tube 10, in the illustrative case, about mm. The spherical bubbles 16, however, will result from the application of higher frequencies of the order of 2025 kc. across the electrodes 12 and 14; while the more oblong bubbles 18 will result from the application of lower frequencies, down around 2500 to 3500 cycles per second. :It will be appreciated that either the spherical bubbles 16 or the oblong bubbles 18 will generally be produced at any one time in a tube but that both types of bubbles will generally not be produced simultaneously.

Referring to F IGUR'E 1(b), the passage of the probe of a voltmeter along the length of the tube 10 shows that the voltage (V of FIGURE l(b)) varies along the length of the tube 10 in the manner of a standing wave 19. The wave form 19 of the voltage V reaches its maxima 20 and minima 22 at points corresponding to the centers of the lighted portions or bubbles 16 or 18 while its zero crossings 24 and the relatively low voltage areas around it correspond to the unlighted portions 26 between the bubbles 16 and 18.

The adjacent ends of adjacent pairs of bubbles have the same polarity and may be seen from FIGURE 1. Furthermore, since each bubble serves as a little tube, one end of the bubble has one polarity and the opposite end of the bubble has the opposite polarity. Since the adjacent ends of adjacent bubbles have the same polarity, the formation of bubbles may be seen. The relatively low pressure in the tube tends to cause clumps of ions to be produced since there are not sufficient ions to produce a uniform ionization in the tube. Furthermore, the ions of the same polarity tend to repel one another to form the bubbles with the spaces 26 between the bubbles having relatively few ions.

From the discussion of FIGURE 1, it can be seen that the broad effect aimed at are the principles and circuitry suitable for deriving a luminescent tube input excitation signal which increases the lighting efficiency and special effects usefulness of luminescent tubes by creating a bubbling effect shown at 16 and 18 in the lighted tube 10 and the additional techniques for causing the bubbles 16 and 18 to move in either direction along the tube and/or to vary their shapes between round 16 and oblong 18.

The first several of the new principles discussed below relate to the generation of gas tube input excitation signals which in various combinations will achieve the bubbling effect. Thereafter, bubbles can be made to progress at various speeds along the length of the luminescent gas tube 10 if the input excitation signal creating the bubbles 16 or 18 has various of its voltage amplitude, current amplitude and frequency increased or decreased at a rate calculated to achieve the desired rate of progress. At the same time, as discussed in connection with the figures to follow, the waveform of each cycle of the input excitation signal must be of such shape that numerous harmonics of the fundamental frequency are applied across the electrodes 12 and 14 of the gas tube 10 and that the potential of the valence electrons of the gas molecules is lowered as much as possible during the negative swing of each cycle. Thus, illumination can be accomplished by gas ionization, rather than by the arcing technique heretofore used. As stated above, ionization, rather than arcing, is important because arcing cannot occur without causing complete illumination of the tube 10 between the electrodes 12 and 14, whereas the bubbling effect is the resultant of a form of incomplete ionization or illumination. Once illumination by ionization is used in place of arcing, the bubbling effect can be achieved by polarizing the tube electrodes 16 and 18 according to their natural anode-cathode potentialities. This waveform issuing from the circuit set forth below is desirable because it is nonsymmetrical about the zero axis. Thereafter, varying different combinations of the input excitation signal current level, voltage or frequency to cause the critical power level for illumination to be slightly undercut will so starve the tube 10 that lighting will be able to occur only in isolated portions of the tube, that is to say, in the lighted bubbles 16 or 18 which have positive and negative ends, as shown by the graph of V in FIGURE l (b), leaving between the lighted portions the dark or only slightly lighted portions 26 across which the voltage does not drop much.

In addition to the input excitation signal principles discussed below, it should be remembered that another feature of applicants invention is the lowering of gas pressure in the lighting tube 10 (when used for creating the bubbling effect) below the pressure normally used, to facilitate achievement of the bubbling effect because of the resultants that arcing is thereby retarded while. ionization is made easier, both due to the thinning out of electron density. The result of this thinning of the luminescent gas is that the individual electrons of the gas molecules have greater freedom of movement and require less energy to ionize or take complete leave of the atomic structure and, accordingly, that the power level of the input excitation signal can be lowered.

Since too high an excitation voltage will cause arcing and since increased excitation frequency agitates the electrons more to give the equivalent of higher pressure, the principles of the invention include the lowering of excitation voltage while raising current amplitude (to increase lighting level) and frequency. This combination gives the ionization and nonarcing type illumination necessary when the bubbling effect is being sought, yet at an acceptable level of brilliance.

Additional inventive features appear in the embodiment of the above-mentioned principles in circuitry for producing a bubbling sign input excitation signal from a standard power supply, preferably a fairly closely regulated one in order that the minute adjustments and shifts necessary to produce bubbles and/or to move them at specified speeds will not be distrubed. Experience has shown that most tubes perform poorly at excitation frequencies below 1,000 c.p.s. and will ionize too fast and grow ineflicient at frequencies above 30 kilocycles, the latter because electron movement has become too erratic and wide. The circuitry for supplying the input excitation signals, therefore, should have first means for converting a power supply signal into a polarized waveform having a certain fundamental frequency in the 1,000 c.p.s., to 25 kc. range and being rich in harmonics of the fundamental and also having a deep negative excursion at one point in each cycle, said first means tending to increase the frequency of the waveform as input power is increased, and further means for varying the overall power (i.e. wattage) applied by the circuit across the lighting tube and also the fundamental frequency of the supply waveform.

Referring to FIGURE 2, the circuit which satisfies these requirements and is the preferred embodiment of several specific circuit principles of applicants invention has for its purpose the application of input excitation signals to the electrodes of the gas tube 10 in such manner that the bubbling effect can be achieved. The gas tube 10 is shown symbolically in the figure; in practive, it would generally be of 10 or so millimeters in diameter and several feet in length. As a feature of the invention, the pressure of the luminescent gas in the tube is made lower than usual to aid in the process. For example, the pressure of the gas in such a 10 mm. diameter tube may be 8 mm. of mercury in contrast to the usual l2-15 mm. Hg. This gas pressure is less than that for producing arcing of the gas in the tube but greater than that for producing glow discharge of the gas in the tube. For example, gas pressures below approximately 3 millimeters are generally considered as the maximum pressures for producing glow discharge of the gas in the tube, whereas gas pressures above approximately 3 millimeters are generally considered as the minimum pressures for producing an ionization of the gas in the tube. A transformer 32 having primary 34 and secondary 36 has the ends of its secondary 36 connected across the electrodes 12 and 14 of the tube 10. A padding capacitor 37 in series with the tube and the secondary 36 presents a lower impedance to the higher harmonics of the input excitation signal supplied by the circuit of FIGURE 2 to facilitate the creation of the bubbles 16 and 18 and also ensures that some impedance appears across the secondary 36 regardless of how low the resistance of the tube 10 is. The padding capacitor 37 also tends to lower the resonant frequency of the circuit including the secondary 36 and the tube 10 so that the creation of bubbles within the tube 10 will be facilitated for reasons which will be explained in detail subsequently. Alternative arrangements of the secondary circuit of the trasformer 32 could do without the padding capacitor 37 and could have one end of the tube 10 grounded and one end of the secondary 36 grounded or could ground one or both and leave the other free-floating. The effects of applicants invention can be achieved with any of these arrangements, and in many situations, the free-floating connection is preferable.

The primary 34 of the transformer 32 has a first end 38 and a second end 39 between which a capacitor 40 is coupled. The capacitor 40 cooperates with the primary 34 of the transformer 32 to form a resonant tank circuit. This tank circuit may have a resonant frequency of approximately 1,000 c.p.s.

The circuitry for supplying input excitation signals through the transformer 32 to the electrodes 12 and 14 of the tube 10 begins with two power supply terminals 42 and 44 which are the output terminals of a source of power that in the practice of the instant invention should be closely regulated in output voltage and substantially ripple-free. The first power supply terminal 42 is directly connected to the first end 38 of the primary 34 of the transformer 32. The second input terminal 44 has coupled to it a resistor 46 which need not be a very large value, but is necessary in the circuit of FIGURE 2 in order to insure that no runaway voltage or current through the circuit destroys the element thereof. Next beyond the current limiting resistor 46, and also essentially at the input to the circuit of FIGURE 2, is a simple filter comprising a capacitor 48 coupled between the resistor 46 and the tfirst power supply terminal 42 and an inductor 49 having a :first end connected to the resistor 46 and the capacitor 48 and having a second end connected to the circuitry to follow.

A silicon-controlled rectifier 50 (hereinafter called an SCR) has an input electrode 52, an output electrode 54 and a gate or control electrode 56. The input electrode 52 is directly connected to the second end of the inductor 49. The output electrode 54 is directly connected to the second end 39 of the primary 34. The circuitry coupled in parallel with the SCR 50 between the inductor 49 and the second end 39 of the primary 34 is specifically concerned with supplying switching signals to the gate or control electrode 56 of the SCR S0.

The timing of the switching signal supplied to the gate 56 of the SCR 50 is determined by an RC circuit comprising a fixed resistor 58, a variable resistor or potentiometer 60 having a movable slide 61, and a time-constant or charging capacitor 62 connected in series between the second end of the inductor 49 and the second end 39 of the primary 34 of the output transformer 32. The capacitor 40 also affects the value of this RC circuit. A semiconductor trigger 64 is connected between the movable slide 61 of the potentiometer 60 and the control electrode 56 of the SCR 50. The operating characteristics of the semiconductor trigger 64 are such that it is nonconductive or off until the charging capacitor 62 reaches its firing voltage (in the practice of the instant invention, about 22 volts), whereupon it fires or switches to its conductive state causing a positive voltage pulse to be supplied to the control electrode 56 of the SCR 50. The operating characteristics of silicon-control rectifiers being what they are, the positive pulse supplied to the gate or control electrode 56 will fire or turn on the SCR to permit current to flow therethrough. Once the SCR S0 is turned on, as long as current flows in the proper direction through the SCR (i.e.from the input electrode 52 to the output electrode 54), the SCR 50 will continue to conduct in spite of the absence of continuing positive voltage on the control electrode 56.

One feature of the instant invention is that the resistance in the RC timing circuit 58-62 is made variable in order to vary the frequency and thus the amount of power passed by the SCR 50. This use of the potentiometer -61 is not found in prior circuitry for supplying luminescent tube input excitation signals. Another feature of the instant invention is the use of a feedback capacitor 66 between the second end 39 of the primary 34 of the output transformer 32 and the gate 56 of the SCR 50 to vary the switching time of the SCR 50 as its frequency of switching varies; for as it is well known, the lighting tube 10 will improve its efiiciency as the frequency of its input excitation signal increases. Therefore, in order to carefully match the power supplied to the lighting tube 10 with the changing efiiciency thereof such that the bubbling effect is created at a wide variety of frequencies, the feedback capacitor 66 is instrumental in switching the SCR 50 on harder and faster at low frequencies to pass more power, while at the higher frequencies a slightly slower switch-on time is provided.

Referring to FIGURE 3, the Waveforms A through E shown there represent the various voltage levels at selected points in the circuit of FIGURE 2 during two cyles of operation, the first cycle running from time z to time t and the second cycle running from time I to 1 The level of the input terminal 42 is taken as the reference level from which the voltages A through E are measured. The voltage A then is taken from the second end of the inductor 49, essentially the input terminal of the excitation signal circuit proper in FIGURE 2. The wave form B is taken at the slide 61 of the potentiometer 60 in the RC time constant circuit, also the input electrode of the trigger 64. The waveform C is the resulting voltage on the output electrode of the trigger 64 and, of course, is the signal applied to the control electrode 56 of the SCR 50. The waveform D in FIGURE 3 is taken from the second end 39 of the primary 34 of the output transformer 32. The waveform E, finally, is the product of the circuit of FIGURE 2: the input excitation signal applied across the electrodes 12 and 14 of the luminescent gas tube 10.

The operation of this circuit can best be considered by beginning with the waveform B, which is primarily the effect of the RC time constant circuit charging between the filter 48-49 and the second end 39 of the primary 34. The rising segment 70 of the waveform B of FIGURE 3 is the result of the capacitor 62 charging through the resistances 58 and 60 toward the voltage of the input power supply terminal 44. It should be noted that the segment 70 starts at a value below the reference voltage 72. The reason for this will be explained below in connection with some of the other waveforms produced by the circuit of FIGURE 2.

When the rising segment 70 of the waveform of FIG- URE B reaches a level 74 suflicient to fire the semiconductor trigger 64, the capacitor 62 discharges through the trigger 64 and, at the same time, has its voltage level pulled down by a decline in the voltage level at the second end 39 of the primary 34. This produces the declining segment 76 of the waveform B of FIGURE 3. The declining segment 76 ends and the rising segment 70 recommences at a bottom level 78 representing the point in time t when the SCR 50 returns fom its conductive to its nonconductive state.

As stated generall above, the firing of the trigger 64 produces a pulse shown at 80 of FIGURE 3(C), said pulse rising in the positive direction above the reference level 82. Since the pulse 80 initiates the switching of the SCR 50, its leading edge 84 is coincident with the t or switch-on time of the SCR 50. The top 86 of the pulse 80 or amplitude thereof is determined by the firing level of the semiconductor trigger 64 and is important in determining the speed of switching the SCR 50 from its nonconductive to its conductive state. The higher the amplitude 86, the quicker the electrons will be removed from the gate zone of the SCR 50 through the gate electrode 56 and thus the quicker full conduction of the SCR 50 will be reached.

As was stated above in connection with the discussion of FIGURE 2, one of the specific circuit features of the instant invention is the placement of the feedback capacitor 66 between the second end 39 of the primary 34 and the output electrode of the trigger 64. It can be seen from the examination of FIGURE 2 that signals fed mack from the point D (i.e., the second end 39 of the primary 34) through the capacitor 66 to the point C would tend to influence the shape of the pulses 80. Moreover, 'due to the lower reactance of the capacitor 66 to higher frequency signals, this feedback influence of the waveform at point D upon the waveform at point C would be greater at higher frequencies of the waveform D. The result of this frequency-variable feedback through the capacitor 66 will be discussed below in connection with the waveform D.

Referring in FIGURE 3(A), the voltage appearing at the input terminal 52 of the SCR 50 will be essentially that of the power supply terminal 44, e until the SCR 50 becomes conductive at time t Once the SCR 50' becomes conductive so that it is essentially closed-circuited to the point D, the voltage at A drops as quickly as the resistor 46 and inductor 49 will permit toward the voltage at point D. This is shown by the segment 88 of the waveform A. The segment 89 of the waveform A begins at t when the input electrode 52 of the SCR 50 returns to the level e of the input terminal 44 as quickly as the inductance 49 and resistance 46 will permit.

Referring to FIGURE 3(D), the effect at the second end 39 of the primary 34 of the output transformer of the circuit of FIGURE 2 of the switching of the SCR 50 can best be seen by tracing the waveform D from the point 90 where the switching-on of the SCR 50 closes the point D to the second terminal 44 of the input power supply. This event causes a great rush of current from the terminal 44 through the SCR 50 and into the capacitor 40 and the primary 34. The effect of current through the primary 34 is the creation of a great reverse EMF which causes the voltage at the second end 39 to make a sudden drop shown by the segment 92 of the waveform D. This drop ends (at 93) only when the SCR 50 turns off, so that the current surge thereto is terminated. After time r with the SCR 50 once more isolating the point D from the second power supply terminal 44, the electrical charge stored in the tank circuit 34-40 initiates a reverse reaction, the first effect of which is the generation of a counter EMF in the primary 34 in response to the discharge current flowing therethrough. This counter EMF is the portion 94 of the waveform D which rises to a high positive voltage before reaching the maximum amplitude 95 of the waveform D. Thereafter, the waveform D declines in essentially a straight line 96 shaped by the discharge of the capacitor 40 until at time t and other currents surge through the SCR 50 begins another cycle of the waveform D.

FIGURE 3(E) shows the wave-shape (i.e., the timevoltage plot over one cycle) produced by the circuit of FIGURE 2 and applied across the electrodes of the gas tube according to one feature of applicants invention. It is similar in shape with the waveform D and begins with the long rise 94e to the high initial level 95e, followed by the linear decay portion 96a of variable length l and variable angle of slope a. At the end of the decay is the deep-negative excursion 92e down to the point 932, from which the voltage later rises to form the leading edge Me of the next individual wave. The purpose of the applied waveform E is to supply energy to the luminescent gas in the tube 10, whereby valence electrons of the individual atoms of the gas are excited out of their normal orbits into some excited orbit. When the electron later returns to its normal orbit, its excess energy is emitted as a quantum of radiation. Accordingly, the high initial level e forces a maximum of energy across the gas at the beginning of each cycle; then the decay 96e imposes an infinitude of harmonics (ranging up to hundreds of 'megacycles in frequency) upon the gas tube electrodes 12 and 14. At certain fundamental frequencies determined by tube diameter, contents and other characteristics, one or more of the higher harmonics in the applied wave-shape of FIGURE 3 (B) will traverse the tube 10 in accordance with the well-known principles of waveguides, whereby the tube 10 will offer greatly reduced attenuation to harmonics above a certain cut-off frequency. Moreover, as is usual with luminescents, the gas in the tube 10' exhibits various spectral characteristics and increased efficacy at certain very small wavelengths, so that variation of the fundamental frequency, by changing the l and the or of the waveform of FIGURE 3(D) will vary the applied harmonics until one appears that brightens the gas tube 10 considerably, at a small expenditure of applied power. The various exact adjustments to reach this optimum condition are to be determined by adjustment using a light-meter.

The negative slope at of the portion 96 and the variable length l of this portion are advantageous for other reasons of some importance. For example, by providing the voltage peak 95, the production of ions in the gas is obtained because of the high energy level produced in the gas. Once ionization has been initiated, the ionization is sustained and further ionization is produced at a reduced energy level. Because of this, the segment 96 can be provided with a negative slope to sustain and produce ionizations without requiring an optimum energy level. This means the energy losses in the tube 10 can be minimized.

The characteristics of the negative excursion 92a in the input voltage waveform of FIGURE 3(E) also provide certain advantages. During the negative excursion, the ions produced in the previous half-cycle are recombined to form molecules such that light is emitted from such recombination as previously described. Furthermore, the excursion 92e is quite sharp and is steeper and greater in amplitude than the positive excursion 94e-96e to insure that the energy level in the tube 10 is reduced below the level where the production and maintenance of ions will be maintained. In this way, the ions produced in each cycle are recombined during the negative excursion 92e so that a new cycle of ionization can be instituted in the next cycle without any holdover of ions from the previous cycle and so that a maximum transfer of energy in the formation of ions and the recombination of ions into molecules can be obtained. Furthermore, the negative excursion 92e is shorter in duration than the positive excursion since it allows an optimum time for ions to be produced and since the level of light in the tube 10 is dependent upon the number of ions produced and the subsequent reformation of these ions into molecules. In view of the fact that the negative portion 92e, 931: and 97e of the voltage wave shape shown in FIGURE 3(E) of the drawings has a different duration, at different wave shape and a different peak amplitude than the positive portion 94c, 95e and 96a of the voltage waveform, the voltage waveform shown in FIGURE 3(E) may be considered as asymmetrica In like manner, the voltage waveform shown in FIGURE 3(E) of the drawings may be considered as asymmetrical. This definition constitutes the manner in which the term asymmetrical is used in the claims. As will be appreciated, an asyml1 metrical waveform is desirable since it is rich in harmonies.

Actually, the wave-shape shown in FIGURE 3(E) has certain other advantages. For example, the deep excursion 92:: in the negative direction causes the rise in voltage from the negative trough 932 of the negative excursion 92a to the peak 95c of the positive excursion 94c to be considerably greater than would otherwise occur for only the positive excursion 94a. This, in turn, causes the increment of energy imparted to the electrons in the molecules to be quite great, so that a high quantum of energy is imparted to the electrons to orbit the electrons through paths considerably removed from the atoms or molecules of which the electrons form a part. This orbiting of the electrons through paths far removed from their atoms or molecules is instrumental in producing the orbiting of additional electrons so that ionization of a considerable number of atoms or molecules occurs. In this way, the amount of light emitted from the tube is considerably enhanced.

The circuit of FIGURE 2 produces and controls the waveform of FIGURE 3(E) in the following manner. Rectified and filtered voltage is applied to the charging capacitor 62 through the resistor 58 and variable resistor 60. When the voltage on the capacitor 62 rises to a particular value, the semiconductor or trigger 64 i caused to conduct, in turn causing gate current (waveform C) to flow to the SCR 50, which then conducts (during the negative-going portion 92 of the negative excursion 92-93-94). The gate current frequency applied to the SCR 50 is controlled by the values of the capacitor 62, resistor 58, variable resistor 60 and the capacitor 40. Accordingly, the output of the trigger 64 operates to modulate the basic tank circuit frequency (determined by the values of the capacitor 40 and the primary 34) that could otherwise be applied to the gas tube 10; for the RC frequency is made several times the resonant frequency of the tank. The choke 49 also supplies part of the negative excursion 92-93-94 of the waveform of FIGURE 3(D) because of the induced voltage thereon at the time the SCR 50 is first turned on, while the collapse of the primary-tank coil 34 gives the waveform a steep, harmonic-rich leading edge and the value of the tank capacitor 40 determines the shape of the decay curve 96, both its length l and angle or.

The circuit shown in FIGURE 2 has certain additional advantages since the length l and the slope at of the portion 96 in FIGURE 3(E) becomes automatically adjusted in accordance with variaions in the characteristics of the tube 10. For example, the impedance of the tube 10 may vary as the tube ages. The circuit shown in FIG- URE 2 automatically varies the length l and the slope or of the portion 96 to compensate for changes in the impedance of the tube 10. The circuit also compensates for variations in the impedance characteristics of different tubes 10, different ambient temperatures, different humidities, etc.

Since the resonant frequency of the tank circuit formed by the primary winding 34 and the capacitor 40 is considerably lower than the charging frequency of the RC circuit formed by the resistor 58, the potentiometer 60 and the capacitors 62 and 40, the tank circuit will be able to undergo only a partial cycle of resonance after the SCR 50 is triggered to a state of conductivity and thereafter to a state of nonconductivity. This means that there will be a charge remaining in the capacitor 40 at the time that a new cycle of charging is instituted in the RC circuit. Since this charge is of a positive polarity, it will bias the trigger 64 against becoming conductivity so that the capacitors 62 and 40 will have to receive increased amounts of charging before the trigger 64 becomes fired and the SCR 50 becomes conductive.

At low rates of charging the capacitors 62 and 40, the resonant frequency of the tank circuit is closer to the effective frequency of the RC charging circuit. This means that the capacitor 40 can discharge more of its charge at these low effective frequencies of the RC charging circuit than at the high effective frequencies of the RC charging circuit. This, in turn, means that the capacitor 40 biases the trigger 64 less at the low charging frequencies than at the high charging frequencies. Because of this, the trigger 64 is fired at a lower voltage across the capacitors 62 and 40 for the low charging frequencies than for the high charging frequencies. This tends to trigger the SCR to the conductive state after a shorter period of time of nonconductivity for low charging rates than for high charging rates. Furthermore, the amount of charge remaining in the capacitor 40 at the initiation of successive charging cycles of the RC circuit tends to vary because the charge remaining in the capacitor 40 at the initiation of each cycle influences the operation of the RC charging circuit in the next cycle, as described above.

In this way, the amplitude of the voltage waveform E in FIGURE 3 and the slope 96 of this voltage Waveform tend to become varied in progressive cycles. As a result, the bubbles produced in the tube 10 may tend to move with time. The rate of movement and the direction of movement of the bubbles are dependent upon the RC time constant of the resistance-capacitance charging circuit. This may be adjusted by adjusting the value of the potentiometer 60 in the circuit shown in FIGURE 2.

As stated above, one of the specific features of the instant invention is the use of the feedback capacitor 66. Now that the waveform D of FIGURE 3 has been explained and the effect on the effective RC charging rate of the remanent charge in the capacitor 40 has been described, the effect of the feedback capacitor 66 upon this waveform can be shown. It can be seen from FIG- URE 2 that the feedback capacitor 66 is electrically connected to feed the voltage signals on the point D back to the point C. Since the feedback capacitor 66 has a substantial impedance at the lower frequencies of the waveform D but somewhat less impedance at the higher frequencies of the waveform D, a smaller portion of the charge remaining in the capacitor 40 is introduced to the trigger 64 at the low effective RC charging rates than at the high effective RC charging rates. This, in turn, sharpens the difference in the charge required in the capacitor 62 and 40 to fire the trigger 64 at the low effective RC charging rates than at the high effective RC charging rates. As a result, the progressive charges in the time required to trigger the SCR 50 in successive cycles is sharpened so as to enhance the effective movement of the bubbles along the tube. As may be seen from the previous paragraphs, the amplitude 95 and the effective slope and length of the portion 96 of the waveform D in FIGURE 3 tend to vary in progressive cycles of operation. This may be seen by comparing the amplitudes 95, 95' and 95" and the slopes 96, 96' and 96" in the waveform D of FIGURE 3. These variations in the shape of the waveform D tend to make the bubbles travel in a manner similar to that described above.

The capacitor 37 also facilitates the production of bubbles for certain important reasons. This results from the fact that the capacitor 37 tends to reduce the resonant frequency of the circuit including the tube 10. Furthermore, since the resonant frequency of the tank circuit formed by the capacitor 40 and the primary 34 is fairly low, the tube 10 receives signals at frequencies which prevent resonant phenomena from occurring in the tube as a whole. However, since each bubble in the tube 10 in effect operates as a little tube within the tube 10, the resonant frequencies in the circuits of the primary 34 and the secondary 36 are such as to facilitate the illumination of gases on a resonant basis within each little tube defined by a bubble.

Of great help in the construction of the transformer 32 is the use of a coil material which at the lower frequencies is inefficient but increases in efficiency as the frequency of signal therethrough increases. This increased efficiency means that at higher frequencies the reverse current fiow due to back EMF in the primary 34 will snap the siliconcontrol rectifier 50 off much more quickly. Thus, the SCR 50 and its timing circuits 5864 are sooner ready to begin another cycle. The high loss of the transformer core at low frequencies means that the SCR 50 can continue working at no-load, low frequency conditions wherein many circuits would tend to decommutate or burn up because of short circuiting. By providing the transformer 32' with a variable impedance at the different frequencies, the impedance of the transformer becomes matched to the impedance of the SCR 50 at the different frequencies. This impedance match prevents the SCR 50 from continuing to conduct through successive cycles of alternating current without any interruption in the current conduction. If the SCR 50 continued to conduct continuously through such successive cycles, it might tend to overheat and become destroyed.

The selection of the value of the tank capacitor 40 is also important to the functioning of the output transformer 32. If the capacitor 40 is to' small, it will not be able to deliver sufficient power; on the other hand, if it is too large, it will not discharge sufiiciently so that the bias provided by the capacitor to the trigger 64 will be excessive, thereby requiring the capacitors 62 and 40 to become charged excessively before the trigger 64 is fired and the SCR 50 is made conductive. Properly selected, however, the capacitor 40 is capable of facilitating the precise starvation of the tube whereby bubbles are formed.

It will be seen from the previous discussion that the values of the resistors 58 and 60 and the capacitors 40 and 62 primarily control the frequency of the repetitive cycles since they control the time at which the trigger 64 becomes conductive; assuming that a constant voltage is produced across the capacitor 48. Of course, since the voltage across the capacitor 48 is being carefully maintained constant as described above, the frequency of the signals produced in the SCR 50 is progressively controlled in the manner described above. The time for initiating each new cycle is controlled in part by the transformer 32 and the charge in the capacitor 40 as described above since the counter EMF produced in the transformer 32 causes a voltage to be introduced through the capacitor 62 to make the trigger 64 non-conductive, and since the counter EMF is dependent in part upon the charge in the capacitor 40. The time required to complete the cycle is dependent in part on the charge in the capacitor 40 since this charge controls the period of time between the triggering of the SCR St) to a state of nonconductivity and the subsequent triggering of the SCR 50 to a state of conductivity.

It will be seen from the discussion of FIGURE 3 that the circuit of FIGURE 2 exemplifies both the broad principles and the specific circuit techniques for achieving the bubbling effect in the luminescent gas tube 10, essentially by starving or depriving the tube 10 of power to a point just below the minimum power level for complete illumination at the frequency of the waveform E at which time the tube 10 is being supplied. In such a situation, the tube 10 can illuminate only partially and this partial illumination finds its stable equilibrium in the form of the bubbles 16 or 18lighted portions having a voltage gradient parallel to the axis of the lighting tube 10 alternating with relatively dark or unlighted portions having little or no voltage gradient along the length of the tube 10. In the absence of sufficient power to illuminate the entire tube 10, a cavitation effect is created whereby only portions of the tube 10 are illuminated and, typically of most equilibrium conditions, these portions are spread evenly and equally throughout the tube 10. These portions, the bubbles 16 and 18 of the instant invention, occupy substantially the full diameter of the tube 1t) and can be made various lengths, oblong, spherical or double oblong (figure eight shaped), depending upon the combined effect of the total wattage of power supplied, the gas pressure within the tube, the frequency of the input excitation signal, and the diameter of the tube 10. Generally speaking, at frequencies around 2,500 to 3,500 cycles per second, the bubbles are oblong; whereas when the frequencies get up toward 25 kilocycles, the bubbles become spherical.

Although the bubbling effect was originally sought mainly for specific effects and advertising purposes where it is desired to attract attention and to supply an interesting and unusual light rather than merely to illuminae some area with a purely functional light source, it has been found that a luminescent tube in which the input excitation signal power has been starved down to the point that the bubbling effect occurs produces light more efficiently (i.e.more lumens of light for each watt of power) than it would when it is receiving sufficient power for full illumination, as stated heretofore, because each separate bubble within the tube functions essentially as a separate tube in its own right. This produces lighting from far tinier tubes than could otherwise be easily produced in the present state of knowledge of luminescent gas tube lighting, and this tiny tube effect gives certain advantages over true gas tubes. The first of these advantages is that a luminescent gas tube experiences about a 50 volt drop in input excitation signal voltage at its electrodes, while the bubble tubes have no electrodes and thus show almost no voltage loss or inefiiciency at all across their ends. Secondly, because of the very short length of these tubes, they are more efficient (usually stated in terms of producing more lumens of light per watt of power consumed) than the full length tube would be. It is the combination of these two advantages that results in the stable equilibrium condition in a luminescent gas tube being the formation of bubbles whenever power is starved below the critical amount required for full length illumination.

The principles for causing the apparent bubbles 16, 18 to move in either direction along the luminescent tube build upon the principles for the formation of bubles accomplished by using an ionization waveform 3E which in each cycle has great richness in harmonics of its fundamental frequency and starving the power content of this waveform below the critical level for full-length illumination of the tube 10. The apparent movement of the bubbles 16 or 18 is then accomplished by shifting the wave form D slightly off its equilibrium position to cause the bubbles to run visibly due to their correspondingly offset or unstable equilibrium position. This results from the shifting of the harmonics spectrum so necessary for ionization and can often be accomplished with greatest ease simply by maintaining the amplitude of the input excitation signal the same while simultaneously varying the potentiometer 60 to shift its registration or its overall voltage level up or down. This shifting of the registration of the input excitation signal D will cause the decay constants of the inductance 34 and capacitances 40 and 62 to aim toward a slightly different zero level, with the result that their decay curves and the numerous frequencies of harmonic distortion composing them would be slightly different than for the equilibrium position where the bubbles 16 or 18 were standing still. The degree of voltage level shift of the input excitation signal E controls the speed of movement and the direction of movement of the bubble formation. In addition, by proper adjustment of the potentiometer 60 (determined by trial and error for each circuit), it has also been found possible to make the bubble formation 16 or 18 move in one portion of the gas tube 10 while standing still in another portion or to move in different directions in opposite ends of the tube It).

A circuit according to the schematic of FIGURE 2 was built and operated using components of the following values:

Power supply:

4244-E :48 Active elements:

50Motorola MCR l3046 64ITT 3 BX 028 Resistors (ohms):

465 .0 S8l0'K 602.SK Capacitors (microfarads):

37-.05 40-.22 48-500 62.Ol5 66-.022 Inductors (millihenries):

Luminescent Gas Tube:

1015 mm. diameter; 12 ft. length Transformer 32:

3416() turns; 363,000 turns While the potentiometer 62 is herein shown to be of the hand-controlled variety for automatic display and advertising applications, electronic circuit means could be substituted to vary the travel behavior of the bubbles 16 or 18 over a series of programmed changes; e.g.frm one direction to another, one speed to another, different behavior in different portions of the tube 10, and combinations of these.

Thus, applicant has achieved the principles and circuitry for deriving a luminescent tube input excitation signal which increases the lighting efficiency and special effects usefulness of luminescent tubes by creating a bubbling effect in the lighted tube and for certain advertising and display uses of the inventive bubble-lighting system provides for making the bubbles to move in either direction along the tube or to vary in shape between round and oblong. The basic bubbling principles relate to the generation of gas tube input excitation signals (waveform of FIGURE 3=( E)) which in various combinations will achieve the bubbling effect 16 or 18; while bubbles 16 or 18 can be made to progress slowly along the length of the luminescent gas tube if the input excitation signal E has its voltage amplitude '95, current amplitude and/ or frequency minutely and carefully increased or decreased, the rate of increase governing the rate of travel of the bubbles 16, 18.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. In combination:

a tube having a sealed envelope of a particular length and having gas in the sealed envelope at a reduced pressure relative to the pressure for producing arcing of the gas in the envelope and at a pressure higher than that for producing a glow discharge of the gas in the tube,

the tube being constructed to obtain light through an ionization of the gas in the envelope rather than through an arcing of the gas in the envelope, and

means electrically connected to the tube for applying signals with particular waveforms to the tube and at frequencies between 1 kilocycle and kilocycles per second to obtain ionization of the gas in the tube in a particular portion in lengths along the tube less than the particular length of the tube whereby 7 full light emission is obtained from the gas in the tube at spaced intervals along the length of the sealed envelope and whereby the light emission from the tube has the appearance of bubbles.

2. In combination:

a lighting tube having a sealed envelope and having only a pair of electrodes disposed at spaced positions in the envelope and having gas in the tube at a reduced pressure with characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, the pressure being reduced relative to that required to produce arcing of the gas in the tube but greater than that for producing a glow discharge of gas in the tube, and

first circuit means electrically connected to the lighting tube and constructed to apply an alternating signal to the electrodes in the lighting tube at variable currents, voltages and frequencies in a range between approximately 1 kilocycle and 25 kilocycles per second, the first circuit means including second circuit means connected to the first circuit means and having characteristics for causing the first circuit means to control the characteristics of current, voltage and frequency of the alternating signal applied to the lighting tube to cause the formation of bubbles and to cause the disposition of the bubbles in the tube to vary.

3. In combination:

a lighting tube having a sealed envelope and having only a pair of electrodes disposed at spaced positions in the tube and having gas in the tube at a reduced pressure with characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, the pressure being reduced relative to that required to produce arcing of the gas in the tube but greater than that for producing a glow discharge of gas in the tube,

first circuit means electrically connected to the lighting tube to apply an asymmetrical, harmonic-rich alternating signal to the lighting tube at variable currents, voltages and frequencies between approximately 1 kilocycle and 25 kilocycles per second, and

second circuit means included in the first circuit means and connected to the first circuit means for controlling the variable current, voltage and frequency of the alternating signal to create intermittently spaced lighted and dark portions in the lighting tube in accordance with such current, voltage and frequency and to control the shape of the intermittently spaced light portions in accordance with the frequency of the alternating signal.

4. In combination:

a tube having a sealed envelope of a particular length and having at least one electrode for conducting an input electrical signal into the sealed envelope and having in the sealed envelope molecules of a luminescent gas with characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, and

circuit means electrically connected to the electrodes in the tube to introduce to the electrode a voltage having a first portion of a first polarity and a second portion of a second polarity opposite to the first polarity with the first portion of the first polarity having a greater duration than the second portion of the second polarity and with the amplitude of the second portion exceeding the amplitude of the first portion, said circuit means including impedance means for varying the voltage introduced to the electrode of the tube through a range causing less than a complete light-emission ionization over the length of the tube such that light is emitted only from particular spaced sectors of the tube to define bubbles.

5. The lighting system according to claim 4, wherein the circuit means include additional impedance means for varying the frequency of the waveform introduced to the electrode of the tube throughout a range between approximately 2,500 cycles per second and 25,000 cycles per second to cause the length of the light emission sectors to decrease from oblong to spherical.

6. In combination:

a tube having a sealed envelope and having gas in the sealed envelope and having a reduced pressure of the gas in the sealed envelope relative to that required to produce arcing of the gas in the tube but having a greater pressure of the gas in the sealed envelope relative to that for producing a glow discharge of the gas in the tube,

means connected to the tube for introducing a signal to the tube with frequency characteristics between approximately 1 kilocycle and 25 kilocycles per second to provide an ionization of the gas in the tube in alternately light and dark portions having the apperance of bubbles and to control the shape of the bubbles in accordance with the applied frequency, and

means connected to the last mentioned means for varying the characteristics of the signal to cause the bubbles to appear to move along the length of the tube at a rate and in a direction dependent upon the variations in the characteristics of the signal.

7. In combination:

a lighting tube having a sealed envelope and having gas in the sealed envelope and having a reduced pressure of the gas in the selaed envelope relative to that for producing arcing of the gas in the tube but greater than that for producing a glow discharge of the gas in the tube,

the tube being constructed to obtain light through an ionization of the "gas in the envelope rather than through an arcing of the gas or a glow discharge of the gas in the enevlope,

first means electrically connected to the tube for providing for ionization of the gas in the tube,

second means associated with the last mentioned means for applying a signal to the first means between approximately 1 kilocycle and 25 kilocycles per second to an ionization of the gas in the tube, and

third means electrically connected to the second means for causing to be produced along the length of the tube alternately ionized and unionized areas having configurations dependent upon the frequency of the signal applied to the first means, said ionized areas having characteristics of providing votage differences along the length of each ionized area and with no difference along the length of each of said unionized areas to obtain no emission of light from each of these unionized areas.

8. In combination in a lighting system:

a power supply constructed to provide a direct voltage, said power supply having first and second output terminals,

a current limiting resistor having first and second terminals, the first terminal of the current limiting resistor being coupled to the first output terminal of the power supply,

a first capacitor connected between the second terminal of the current limiting resistor and the second output terminal of the power supply,

an inductor having first and second tenminals, the first terminal of the inductor being connected to the second terminal of the current limiting resistor,

a silicon controlled rectifier having an input electrode, an output electrode and a control electrode, the input electrode of the silicon controlled rectifier being connected to the second terminal of the inductor,

a time constant resistor having first and second terminals, the first terminal of the first resistor being connected to the second terminal of the inductor,

a variable resistor having first and second terminals and a movable slide, the first terminal of the variable resistor being connected to the second terminal of the time constant resistor,

a second capacitor having first and second terminals,

the first terminal of the second capacitor being connected to the movable slide of the variable resistor and the second terminal of the second capacitor being connected to the output terminal of the silicon controlled rectifier,

a semiconductor trigger having an input electrode and an output electrode, the input electrode of the semiconductor trigger being connected to the movable slide of the variable resistor and the output electrode of the semiconductor trigger being connected to the gate electrode of the silicon controlled rectifier,

a third capacitor connected between the second terminal of the second capacitor and the output electrode of the semiconductor trigger,

an output transformer having a primary winding and a secondary winding, the primary winding of the output transformer having first and second terminals and the secondary Winding of the output trans former having first and second terminals, the first terminal of the primary Winding being connected to the second output terminal of the power supply and the second end of the primary winding being connected to the output electrode of the silicon controlled rectifier,

a fourth capacitor connected between the first and second terminals of the primary of the output transformer,

a fifth capacitor having first and second terminals,

the first terminal of the fifth capacitor being connected to the first terminal of the secondary of the output transformer, and

a tube having a sealed envelope of a particular length and having first and second electrodes and having gas in the tube with characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, the tube and the gas in the tube having characteristics to provide resonances in the tube at particular frequencies constituting harmonics of one another and to provide ionization of the gas in bubbles spaced along the length of the tube in accordance with the amount of power applied to the tube, the first electrode of the tube being connected to the second terminal of the fifth capacitor and the second electrode of the tube being connected to the second terminal of the secondary of the output transformer.

9. In combination:

a tube having a sealed envelope of a particular length and having at least one electrode for conducting an input electrical signal into the sealed envelope and having in the sealed envelope molecules of a luminescent gas with characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, and

circuit means electrically connected to the electrode in the tube to introduce to the electrode a voltage having a waveform with a first portion of a first polarity and a second portion of a second polarity opposite to the first polarity with a lesser duration, but a greater amplitude than the first portion of the first polarity, and means included in said circuit means for obtaining variations in the frequency of the waveform introduced to the electrode of the tube throughout a range causing progressive ionization over the length of the tube from a condition of ionization in relatively small portions of the particular length of the tube through conditions of ionization of different portions of the length of the tube in accordance with such variations in frequency.

10. In combination:

a tube having a sealed envelope and having gas in the sealed envelope and having a reduced pressure of the gas in the sealed envelope relative to that required to produce arcing of the gas in the tube but having a greater pressure of the gas in the tube than that for producing a glow discharge of the gas in the tube,

the tube being constructed to obtain light through an ionization of the gas in the envelope rather than through an arcing or a glow discharge of the gas in the envelope,

first means electrically connected to the tube for applying a signal between approximately 1 kilocycle and 25 kilocycles per second to the tube to obtain an ionization of the gas in the tube, and

means electrically connected to the first means for cooperating with the first means to obtain an ionization of the gas in the tube only at spaced intervals along the length of the tube for the formation of bubbles at progressive intervals along the length of the tube with configurations dependent upon the frequency of the signal applied to the tube.

11. In combination in a lighting system:

a power supply constructed to provide an output voltage, said power supply having first and second output terminals,

a silicon controlled rectifier having an input electrode, an output electrode and a control electrode, the input electrode of the silicon controlled rectifier being connected to the first output terminal of the power pp y,

a time constant resistor having first and second terminals, the first terminal of the first resistor being connected to the first output terminal of the power pp y,

a variable resistor having first and second terminals and a slide movable between such first and second terminals, the first terminal of the variable resistor being connected to the second terminal of the time constant resistor,

a first capacitor having first and second terminals, the first terminal of the first capacitor being connected to the movable slide of the variable resistor and the second terminal of the first capacitor being connected to the output terminal of the silicon controlled rectifier,

a semiconductor trigger having an input electrode and an output electrode, the input electrode of the semiconductor trigger being connected to the movable slide of the variable resistor and the output electrode of the semi-conductor trigger being connected to the control electrode of the silicon controlled rectifier,

an output transformer having a primary winding and a secondary winding, the primary winding of the output transformer having first and second terminals, the first terminal of the primary winding being connected to the second output terminal of the power supply and the second terminal of the primary winding being connected to the output electrode of the silicon controlled rectifier,

a second capacitor connected between the first and second terminals of the primary of the output transformer,

a tube having a sealed envelope of a particular length and having first and second electrodes and having gas in the tube with characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, the tube and the gas in the tube having characteristics to provide resonances in the tube at particular frequencies constituting harmonics of one another and to provide ionization of the gas in the tube in bubbles spaced along the length of the tube in accordance with the amount of power applied to the tube, the electrodes of the tube being connected across the first and second terminals of the secondary of the output transformer.

12. In combination:

a tube having a sealed envelope and having gas in the sealed envelope and having a reduced pressure of the gas in the sealed envelope relative to that for producing arcing of the gas in the envelope but having a greater pressure of the gas in the tube than that for producing a glow discharge of the gas in the tube, the tube being constructed to obtain light through an ionization of the gas in the envelope rather than through an arcing or a glow discharge of the gas in the envelope,

first means electrically connected to the tube for supplying an input electrical excitation signal at frequencies between approximately 1 kilocycle and 25 kilocycles per second to obtain an ionization of the gas in the tube,

second means electrically connected to the first means for cooperating with the first means to create an ionization of the gas in the tube only at spaced lengths less than the total length of the tube and with configurations dependent upon the frequency of the signal applied to the tube for the emission of light from the tube at the position of the ionization of the gas in the tube whereby the light emission from the tube has the appearance of bubbles, and

third means electrically connected to the second means for varying the operation of the second means to cause apparent travel of the bubbles in the tube.

13. In combination in a lighting system:

a first active element having an input electrode, an output electrode and a control electrode,

a first capacitor having first and second terminals, the first terminal of the first capacitor being connected to the output terminal of the first active element,

a second active element having an input electrode and an output electrode, the input electrode of the second active element being connected to the second terminal of the first capacitor and the output electrode of the second active element being connected to the control electrode of the first active element to obtain an operation of the second active element upon the occurrence of a particular charge in the first capacitor,

an output transformer having a primary winding and a secondary winding, the primary winding being connected to the output electrode of the first active eie ment,

at second capacitor connected across the primary of the output transformer,

means for applying a voltage to the first capacitor and to the input electrode of the first active element and the primary winding of the output transformer to obtain a charging of the capacitor to the first particular value and an operation of the first active element upon the operation of the second active element, and

a tube having a sealed envelope of a particular length and having first and second electrodes and having gas in the tube With characteristics of becoming ionized and of obtaining an emission of light upon becoming ionized, the gas in the tube having characteristics to provide resonances in the tube at particular frequencies constituting harmonics of one another and to provide ionization of the gas in bubbles spaced along the length of the tube in accordance with the amount of power of the signals applied to the tube, the electrodes of the tube being connected across the secondary of the output transformer to obtain an ionization of the gas in the tube upon the operation of the first active element.

14. In combination:

a tube having a sealed envelope and having gas in the sealed envelope with properties of becoming ionized 21 upon a resonance of the gas at a particular frequency,

first electrical circuit means including an inductor and a first capacitor connected to each other to provide resonance of the first electrical circuit means and the gas in the tube at the particular frequency,

second electrical circuit means including a resistor and a second capacitor connected to each other and to the first electrical circuit means to provide an RC time constant representing a frequency greater than the resonant frequency of the first electrical circuit and to provide a resonance of the first electrical circuit means at the particular frequency,

a switching member,

and third electrical circuit means connected to the first and second electrical circuit means and to the switching member for alternately producing states of conductivity and non-conductivity in the switching member at a rate at each instant dependent upon the RC time constant and upon the difference in frequency between the frequency represented by the RC time constant and the resonant frequency of the first electrical circuit means to establish in the first electrical circuit means an alternating signal at the particular frequency, and

means connected to the tube and responsive to the alternating signals with the particular characteristics from the first electrical circuit means for facilitating ionizations of the gas at spaced intervals in the tube to obtain in the tube an illumination representing bubbles.

15. The combination set forth in claim 14 wherein:

adjustable means are included in the second electrical circuit means for providing adjustments for the RC time constant to control the movements of the bubbles within the tube.

16. In combination:

a tube having a sealed envelope and having gas in the sealed envelope at a particular pressure to produce ionization of the gas in the tube and resonances of the gas in the tube at a particular frequency,

a first capacitor and an inductor connected to form a circuit resonant at the particular frequency,

a switching member having conductive and non-conductive states and connected to the first capacitor and the inductor to control the introduction of energy 22 into the inductor and the capacitor during the conductive state of the switching member,

a trigger having conductive and non-conductive states and connected to the switching member to obtain an operation of the switching member in the conductive state upon the firing of the trigger to the conductive state and connected to the first capacitor to be biased against a state of non-conductivity by the charge in the first capacitor,

a resistor and a second capacitor connected to the first capacitor to provide an RC circuit with a time constant representing a frequency greater than the resonant frequency of the first capacitor and the inductor, the resistor and the second capacitor being con nected to the trigger to fire the trigger into a state of conductivity upon the occurrence in the first and second capacitors of charges overcoming the bias on the trigger,

means connecting the switching member, the first and second capacitors, the trigger and the resistor in electrical circuitry for producing alternate states of conductivity and non-conductivity in the trigger and accordingly in the switching member to obtain the production of an alternating signal with particular characteristics in the resonant circuit formed by the inductor and the first capacitor, and

means connected to the tube and responsive to the alternating signal in the first resonant circuit to produce in the tube an ionization at spaced intervals along the length of the tube for the production of bubbles of illumination in the tube.

17. The combination set forth in claim 16, wherein the resistor is adjustable in value to provide for the movements of the bubbles in either of two opposite directions in the tube.

References Cited UNITED STATES PATENTS 2,091,953 9/1937 Becquemont 315-108 JOHN W. HUCKERT, Primary Examiner.

JERRY D. CRAIG, Assistant Examiner.

US. Cl. X.R. 

